Mechanical property, biocorrosion and in vitro biocompatibility evaluations of Mg–Li–(Al)–(RE) alloys for future cardiovascular stent application

Mg–Li-based alloys were investigated for future cardiovascular stent application as they possess excellent ductility. However, Mg–Li binary alloys exhibited reduced mechanical strengths due to the presence of lithium. To improve the mechanical strengths of Mg–Li binary alloys, aluminum and rare earth (RE) elements were added to form Mg–Li–Al ternary and Mg–Li–Al–RE quarternary alloys. In the present study, six Mg–Li–(Al)–(RE) alloys were fabricated. Their microstructures, mechanical properties and biocorrosion behavior were evaluated by using optical microscopy, X-ray diffraction, scanning electronic microscopy, tensile tests, immersion tests and electrochemical measurements. Microstructure characterization indicated that grain sizes were moderately refined by the addition of rare earth elements. Tensile testing showed that enhanced mechanical strengths were obtained, while electrochemical and immersion tests showed reduced corrosion resistance caused by intermetallic compounds distributed throughout the magnesium matrix in the rare-earth-containing Mg–Li alloys. Cytotoxicity assays, hemolysis tests as well as platelet adhesion tests were performed to evaluate in vitro biocompatibilities of the Mg–Li-based alloys. The results of cytotoxicity assays clearly showed that the Mg–3.5Li–2Al–2RE, Mg–3.5Li–4Al–2RE and Mg–8.5Li–2Al–2RE alloys suppressed vascular smooth muscle cell proliferation after 5 day incubation, while the Mg–3.5Li, Mg–8.5Li and Mg–8.5Li–1Al alloys were proven to be tolerated. In the case of human umbilical vein endothelial cells, the Mg–Li-based alloys showed no significantly reduced cell viabilities except for the Mg–8.5Li–2Al–2RE alloy, with no obvious differences in cell viability between different culture periods. With the exception of Mg–8.5Li–2Al–2RE, all of the other Mg–Li–(Al)–(RE) alloys exhibited acceptable hemolysis ratios, and no sign of thrombogenicity was found. These in vitro experimental results indicate the potential of Mg–Li–(Al)–(RE) alloys as biomaterials for future cardiovascular stent application and the worthiness of investigating their biodegradation behaviors in vivo.